Dramatic response of a BRAF V600E-mutated primary CNS histiocytic sarcoma to vemurafenib

Diagnostic challenges of primary central nervous system histiocytic sarcoma: case report and literature review

Histiocytic sarcoma (HS) is a rare malignant tumor that primarily affects the lymph nodes, intestines, skin, and soft tissues. Primary central nervous system histiocytic sarcoma (PCNSHS) is even rarer. We present the case of a 50-year-old Asian male with PCNSHS who was hospitalized after experiencing intermittent headaches and slurred speech for a week. During surgery, both tumor cells and purulent material were observed, and the diagnosis of PCNSHS was ultimately confirmed by immunohistochemistry. Furthermore, we conducted a literature review from 1952 to the present, screening and analyzing 49 related cases across 41 publications.

Monocytic meningitis complicating histiocytosis and response to MEK-inhibitor: a case series

Central nervous system (CNS) involvement is common in histiocytosis, yet cerebrospinal fluid (CSF) analysis often yields normal results. We present three cases of monocytic meningitis associated with histiocytosis. The first patient was diagnosed with Erdheim-Chester disease (ECD) and exhibited evidence of a MAP2K1 mutation, concomitant with chronic myelomonocytic leukemia. Brain magnetic resonance imaging (MRI) revealed leptomeningitis and pachymeningitis. The presence of the same MAP2K1 mutation in CSF monocytes confirmed the clonal origin of neuromeningeal infiltration. Treatment with binimetinib rapidly improved the patient's clinical condition. The second case involved CNS primary malignant histiocytosis (CNS-PMH) associated with myelodysplastic syndrome. However, treatment with binimetinib only led to a partial and time-limited response. The last patient was diagnosed with mixed histiocytosis ECD/Rosai-Dorfman disease (RDD). Cobimetinib also proved effective in managing CNS symptoms. CSF pleocytosis in CNS involvement of histiocytosis has been reported in a few published cases with neurological involvement. Given its rarity, the presence of monocytic meningitis should prompt immediate suspicion of histiocytosis, particularly if accompanied by typical manifestations. In cases of neurological involvement in histiocytosis, lumbar puncture and liquid biopsy can sometime overcome the need for a meningeal biopsy. The molecular characterization of histiocytosis is essential for considering the use of targeted therapy, but the lack of an identified mutation should not preclude the use of anti-MEK therapy.

Case report: Treatment of a rare primary cerebellum histiocytic sarcoma with surgery and radiotherapy

Background

Histiocytic sarcoma originates in various tissues, including the skin, lymph nodes, gastrointestinal tract, lungs, bone marrow, and central nervous system. Primary central nervous system histiocytic sarcoma (PCNSHS) is exceptionally rare, known for its aggressive behavior and poor prognosis. This report describes a case of PCNSHS in the cerebellum treated with surgery and radiotherapy.

Case presentation

A 30-year-old woman presented with progressive dizziness and headache. Magnetic resonance imaging scans showed right cerebellar neoplastic lesions approximately 3.6 cm*3.0 cm with cerebral edema and fourth ventricle and brainstem compression. The patient underwent surgical debulking, and the pathological diagnosis was PCNSHS. Two months after the surgery, the patient underwent adjuvant radiotherapy at a dose of 60 Gy. No tumor progression has been observed during the one-year follow-up period.

Conclusions

This case report provides an example of effective central nervous system control using resection and radiation therapy. A review of the literature confirms that surgery alone or combined concurrent or sequential treatment of radiotherapy and chemotherapy is often used; however, the best treatment plan remains unclear. Moreover, the prognosis is poor, with a median survival of six months. Thus, ongoing research aims to better understand the biology of histiocytic sarcomas and find more effective strategies.

Histiocytic sarcoma affecting the oral cavity: a clinical, pathologic and molecular study

OBJECTIVE

To investigate the clinicopathological, immunohistochemical and molecular features of histiocytic sarcomas affecting the oral cavity.

METHODS

Pathology files of two institutions were searched for cases of histiocytic sarcoma, and new H&E-stained slides and immunohistochemistry reactions evaluated for diagnosis confirmation. Molecular screening for KRAS and PIK3CA mutations was performed through polymerase chain reaction (PCR) followed by Sanger sequencing. BRAFp.V600E mutation was assessed by pyrosequencing. Clinical data regarding sex, age, tumor location, systemic manifestations, clinical presentation, follow-up time, treatment applied and status at last follow-up were collected from patients' pathology and medical files.

RESULTS

Three cases were retrieved during the period investigated (2000-2023). Two females and one male were affected, with a wide age range, involving the tongue, palate and gingiva. Histopathologically, the neoplasms presented as highly pleomorphic atypical cells distributed diffusely with infiltration of normal structures. All cases demonstrated histiocytic differentiation expressing CD68 and CD163, and a high Ki67 expression. Genetic mutations were evaluated in two cases. One case harboured BRAF-V600E mutation, but not in KRAS and PIK3CA, while the second case did not show mutation in BRAF-V600E, KRAS and PI3KCA. One patient was lost, and two patients died after eight and four months of follow-up.

CONCLUSION

Histiocytic sarcomas involving the oral cavity are extremely rare, and may represent dissemination of a systemic condition. It has an aggressive biological behaviour with a poor overall prognosis.

Population Pharmacokinetics, Pharmacodynamics and Safety Properties of Trametinib in Dogs With Cancer: A Phase I Dose Escalating Clinical Trial

MAPK has been reported as a key oncogenic pathway for canine histiocytic sarcoma, which can be pharmacologically targeted with trametinib, a small inhibitor of MEK1/2. Preliminary data showed promising antitumor activity in in vitro and in vivo models and represented a proof of concept to translate the findings from bench to bedside. In this phase I, dose escalating study using a 3 + 3 cohort design, trametinib was evaluated in 18 dogs with cancer. Adverse events were graded according to VCOG-CTCAE v2. Blood samples and tumour biopsies were collected for pharmacokinetic and pharmacodynamic assessment. Trametinib was well tolerated with a maximum tolerated dose of 0.5 mg/m2/day, PO. Dose-limiting toxicities included systemic hypertension, proteinuria, lethargy and elevated ALP, and were all Grade 3. The drug exposures increased more than linearly with dose since the elimination of trametinib was saturable. At a dose of 500 μg Q24h (0.5 mg/m2/day in a 30 kg dog), approximately 70% of dogs had an average steady-state concentration of 10 ng/mL, achieved after approximately 2 weeks. This threshold was associated with clinical efficacy in humans. Target engagement was not observed in biospecimens collected on Days 0 and 7. In conclusion, trametinib was considered safe in dogs with cancer, and the dose of 0.5 mg/m2/day was the recommended dose for phase II studies.

Rapid but nondurable response of a BRAF exon 15 double-mutated spindle cell sarcoma to a combination of BRAF and MEK inhibitors

INTRODUCTION

BRAF V600E substitution predicts sensitivity of a cancer to BRAF inhibitor therapy. The mutation is rarely found in soft-tissue sarcomas. Here we describe a case of undifferentiated spindle cell sarcoma showing primary insensitivity to standard chemotherapy and pronounced but non-sustained response to BRAF/MEK inhibitors at recurrence.

CASE PRESENTATION

A 13-year-old girl was diagnosed with low-grade spindle cell sarcoma of pelvic localization, BRAF exon 15 double-mutated: c.1799T>A p.V600E and c.1819T>A p.S607T in cis-position. The tumor showed resistance to CWS-based first-line chemotherapy and was treated surgically by radical resection. Seven months after surgery the patient developed metastatic relapse with abdominal carcinomatosis. Combined targeted therapy with BRAF/MEK inhibitors afforded complete response in 1 month and was continued, though complicated by severe side effects (fever, rash) necessitating 1-2 week toxicity breaks. After 4 months from commencement the disease recurred and anti-BRAF/MEK regimen consolidation was unsuccessful. Intensive salvation chemotherapy was ineffective. Empirical immunotherapy afforded a transient partial response giving way to fatal progression with massive, abdominal cocoon-complicated peritoneal carcinomatosis.

CONCLUSION

This is the first report of spindle cell sarcoma BRAF V600E/S607T double-mutated, responding to a combination of B-Raf and MEK inhibitors. Despite the low histological grade and radical surgical treatment of the tumor at primary manifestation, the disease had aggressive clinical course and the response to BRAF/MEK targeted therapy at recurrence was complete but nondurable. Empirical use of pembrolizumab provided no unambiguous evidence on the clinical relevance of immunotherapy in protein kinase -rearranged spindle cell tumors.

Long-Term Remission with Novel Combined Immune-Targeted Treatment for Histiocytic Sarcoma Accompanied by Follicular Lymphoma: Case Report and Literature Review

Histiocytic sarcoma (HS) is an extremely rare but aggressive hematopoietic malignancy, and the prognosis has been reported to be rather unfavorable with a median overall survival of merely 6 months. We presented a 58-year-old female patient complaining of abdominal pain and fever, who was admitted to our institution in September 2021. Fluorine-18-fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET/CT) scan showed enlargement of generalized multiple lymph nodes. Subsequently, laparoscopic retroperitoneal lesion biopsy and bone marrow aspiration were performed. The pathological findings indicated the diagnosis of HS concurrent with follicular lymphoma. The immunohistochemistry (IHC) staining of the tumor lesion revealed a high expression of CD38 and PD-L1 proteins. Furthermore, KRAS gene mutation was identified by means of next-generation sequencing. The patient exhibited poor treatment response to both first- and second-line cytotoxic chemotherapies. Therefore, she underwent six cycles of Daratumumab (anti-CD38 monoclonal antibody), Pazopanib (multi-target receptor tyrosine kinases inhibitor) combined with third-line chemotherapy, followed by involved-site radiotherapy and maintenance therapy with the PD-1 inhibitor Tislelizumab. Long-term partial remission was finally achieved after multi-modality treatment. Duration of remission and overall survival reached 22 and 32 months, respectively. Our case indicated that immuno-targeted treatment coupled with chemotherapy and radiotherapy might constitute a potential therapeutic option for HS.

One Health: Therapies Targeting Genetic Variants in Human and Canine Histiocytic and Dendritic Cell Sarcomas

The precise cause of HS/DCS is still unknown. The relatively low incidence in humans urges for an animal model with a high incidence to accelerate knowledge about genetics and optimal treatment of HS/DCS. Namely, until now, the therapies targeting genetic variants are still more experimental and sparsely used, while consensus is missing. In addition, the literature about variants and possible mutation-targeted therapies in humans and dogs consists mainly of case reports scattered throughout the literature. Therefore, an overview is provided of all currently known genetic variants in humans and dogs with HS/DCS and its subtypes, their possible mutation-targeted therapies, their efficacy, and a contemplation about the future. Several genetic variants have already been discovered in HS/DCS, of which many are shared between canine and human HS/DCS, but unique variants exist as well. Unfortunately, none of these already found variants seem to be specifically causal for HS/DCS, and the puzzle of its landscape of genetic variation is far from complete. The use of mutation-targeted therapies, including MAPK-/MEK-inhibitors and the future use of PTPN11-, CDK4/6- and PD-1-inhibitors, seems to be promising for these specific variants, but clearly, clinical trials are needed to determine optimal inhibitors and standardised protocols for all variants. It can be concluded that molecular analysis for variants and subsequent mutation-targeted therapy are an essential addition to cancer diagnostics and therapy. A joint effort of humans and dogs in research is urgently needed and will undoubtedly increase knowledge and survival of this devastating disease in dogs and humans.

Clinical characteristics, molecular aberrations, treatments, and outcomes of malignant histiocytosis

Malignant histiocytosis (MH) is an extremely rare neoplasm of the macrophage-dendritic cell lineage. We report the clinical characteristics, molecular aberrations, treatments, and outcomes of patients with MH seen at two referral centers from January 2000 to May 2023. We identified 43 patients with MH, of which 26 had histiocytic sarcoma (MH-H), 9 interdigitating dendritic cell sarcoma (MH-IDC), and 8 Langerhans cell sarcoma (MH-LC). The median age at diagnosis was 61 years (range, 3-83). Thirty-three patients (77%) had multifocal disease, while 10 had unifocal involvement. Tumor specimens from 22 patients (51%) underwent targeted next generation sequencing, and 19 of 22 (86%) had at least one pathogenic mutation, including mutations in MAPK pathway genes (73%). The median overall survival (OS) among the entire cohort was 16 months (95% CI: 8-50). The outcomes of those with multifocal disease were significantly shorter than their unifocal counterpart: median OS of 10 months versus 50 months (p = .07). Patients with risk organ involvement (bone marrow, spleen, or liver) had significantly inferior outcomes. Chemotherapy and surgery were the most common first-line treatments for multifocal and unifocal disease, respectively. While the outcome for patients with multifocal disease was poor, there was a subset of patients who had durable responses to treatment. Our study highlights that MH has heterogeneous clinical presentation, frequent oncogenic mutations, and prognosis, which is strongly tied to disease extent and type of organ involvement.

Primary pulmonary histiocytic sarcoma with high PD-L1 expression benefited from immunotherapy: A case report and bioinformatic analysis

Histiocytic sarcoma is an aggressive haematopoietic malignancy accounting for less than 1% of haematolymphoid neoplasms with a diagnosis based on morphology and immunophenotype of tissue biopsies with a very poor prognosis. Here, we report a 45-year-old man who was diagnosed with primary pulmonary histiocytic sarcoma with systemic metastases, with partial remission (PR) treated with cyclophosphamide, doxorubicin, vincristine and prednisone (CHOP) chemotherapy, but it relapsed soon after therapy above. Tests demonstrated that TMB was 21 Muts/Mb PD-L1 expression was 90% positive, and the disease has been well-controlled over 3 years using immune checkpoint inhibitors (nivolumab and pembrolizumab). Bioinformatic pan-cancer analysis verified that there was the highest genetic alteration frequency of PD-L1 in which amplification accounted for the majority of sarcoma tumour samples. Following that, we found that the genetic alteration of PD-L1 was associated with poor prognosis in sarcoma patients in terms of overall survival (OS) (p = 1.51 × 10-4 ), progress-free survival (PFS) (p = 4.90 × 10-2 ) and disease-specific survival (DSS) (p = 4.90 × 10-2 ). To our knowledge, this may be the first reported case with high PD-L1 expression in primary pulmonary histiocytic sarcoma who may benefit from immunotherapy such as nivolumab and pembrolizumab significantly and safely.

A rare case of primary central nervous system histiocytic sarcoma harboring a novel ARHGAP45::BRAF fusion: a case report and literature review

INTRODUCTION

Patients with histiocytic sarcoma occurring in the central nervous system (CNS) are rare and have a very poor prognosis. The increased use of molecular diagnostic approaches in solid tumors has brought more opportunities for the diagnosis and treatment of central nervous system histiocytic sarcoma (CNSHS).

CASE DESCRIPTION

A 9-year-old girl was admitted to the hospital with pain in her head and neck, as well as vomiting. Imaging scans showed a prominent abnormality in the anterior falciform region, and histopathology revealed the presence of CD68 (+) and CD163 (+) cells, leading to a preliminary diagnosis of primary intracerebral CNSHS. Molecular profiling tests identified a new variant of ARHGAP45::BRAF fusion in this case, which has not been reported in any other tumor. The patient underwent surgical removal of the tumor and will require long-term monitoring.

CONCLUSION

The presence of the BRAF point mutation, predominantly BRAF p.V600E, has been documented in prior literature of CNSHS. This is the first case of pediatric histiocytic sarcoma in the anterior falciform region who has a unique ARHGAP45::BRAF fusion. The findings of our study indicate that a broader range of molecular assays should be employed in the diagnosis of CNSHS and opens up new possibilities for the treatment of the patient.

Favorable outcome of a histiocytic sarcoma patient treated with immune checkpoint inhibitor: a case report

Introduction and Importance

Histiocytic sarcoma (HS) is an extremely rare malignancy in which there has been no standard treatment approach. Some preclinical studies have provided rationales for the application of immunotherapy in advanced HS.

Case Presentation

The authors reported a case of a 61-year-old patient with metastatic HS who had a rapid progression on ifosfamide, carboplatin, and etoposide chemotherapy. The authors performed PD-L1 testing, which showed a strong positivity in 90% of tumor cells. The patient was then treated with pembrolizumab 200 mg every 3 weeks. He refused palliative radiotherapy. A dramatic response in all sites was recorded on the PET-CT scan after three cycles. He was maintained on pembrolizumab, reaching over 30 months without disease progression.

Clinical Discussion

Recent molecular data suggests there could be a role of immunotherapy in HS. In our patient, the disease was refractory to chemotherapy and pembrolizumab has been given based on the strong PD-L1 expression. Response to immunotherapy has also been recorded in several cases with malignant histiocytic neoplasm.

Conclusion

Immunotherapy might bring sustained disease remission in PD-L1 high expression HS and further studies evaluating the role of immune checkpoint inhibitor in this disease are warranted.

Primary intracranial histiocytic sarcomas: a report of six cases and a pooled analysis of individual patient data

OBJECTIVE

Primary intracranial histiocytic sarcomas (PIHSs) are extremely rare with limited reported cases, making their prognostic factors and management uncertain. This study aims to describe the clinical characteristics of PIHSs and propose a treatment protocol for this entity.

METHODS

Clinical data were collected from six patients diagnosed with PIHSs at Beijing Tiantan Hospital between March 2011 and October 2022. Additionally, a comprehensive search of the PubMed database was conducted using the keywords "primary intracranial" or "primary central nervous system" combined with "histiocytic sarcoma" or "histiocytic sarcomas" between 1996 and 2022, identifying 24 cases. A pooled analysis of individual patient data was performed to assess risk factors for overall survival (OS).

RESULTS

The six cases included four males and two females, with a mean age of 42.2 ± 13.3 years. In total, 24 cases of PIHSs were identified from previous studies. Multivariate Cox regression analysis revealed that gross total resection (GTR) was the only factor predicting a longer OS (p = 0.027). Kaplan-Meier analysis demonstrated that GTR (p = 0.0013), solitary lesions (p = 0.0048), and radiotherapy (p = 0.0492) were associated with a longer OS.

CONCLUSION

PIHSs are rare brain tumors with poor clinical prognosis. Patients with solitary lesions have a longer OS than those with multifocal lesions. Gross total resection must be the first choice. Radiotherapy may bring benefits for these patients, but chemotherapy may not be useful. Further studies involving larger cohorts are necessary to validate these findings.

Neurological Manifestations of Histiocytic Disorders

PURPOSE OF REVIEW

Histiocytic disorders, including Erdheim-Chester disease (ECD), Langerhans cell histiocytosis (LCH), and Rosai-Dorfman disease (RDD), are rare neoplasms that may present with a spectrum of neurologic involvement. Diagnostic delay is common due to heterogeneity in presentation and challenging pathology.

RECENT FINDINGS

Recent advances in the treatment of these diseases targeted towards mutations in the MAP kinase pathway have led to an improved prognosis in these patients with neurologic involvement. It is critical for clinicians to have a high index of suspicion to allow for early targeted treatment and optimize neurologic outcomes. A systematic approach to diagnosis is presented in this article to allow for accurate diagnosis of these rare diseases.

Treatment of Langerhans Cell Histiocytosis and Histiocytic Disorders: A Focus on MAPK Pathway Inhibitors

Histiocytic disorders are rare diseases defined by the clonal accumulation of a macrophage or dendritic cell origin. These disorders include Langerhans cell histiocytosis, Erdheim-Chester disease, juvenile xanthogranuloma, malignant histiocytoses, and Rosai-Dorfman-Destombes disease. These histiocytic disorders are a diverse group of disorders with different presentations, management, and prognosis. This review focuses on these histiocytic disorders and the role of pathological ERK signaling due to somatic mutations in the mitogen--activated protein kinase (MAPK) pathway. Over the last decade, there has been growing awareness of the MAPK pathway being a key driver in many histiocytic disorders, which has led to successful treatment with targeted therapies, in particular, BRAF inhibitors and MEK inhibitors.

A Rare Case of Pediatric Xanthoma Disseminatum With Diabetes Insipidus and BRAF p.V600E Mutation

ABSTRACT

Xanthoma disseminatum (XD) is a rare non-Langerhans cell histiocytosis characterized by xanthomatous lesions in the absence of hyperlipidemia. XD usually develops in young adults, and there are rare cases among children. BRAF mutations are frequent in Langerhans cell histiocytosis and Erdheim-Chester disease but absent or only rarely detected in other histiocytosis. Herein, we described a 6-year-old Chinese girl presented with generalized skin lesions and diabetes insipidus for 5 months. There were multiple periorbital xanthelasma with histopathological features of foamy histiocytes infiltration with Touton cells. Pituitary magnetic resonance imaging showed pituitary enlargement and pituitary stalk thickening. The presence of BRAF p.V600E mutation makes this case distinctive and also offers a potential therapeutic target. According to our review of the literature, this is the first pediatric XD with diabetes insipidus and BRAF mutation.

Case Report: Long-Term Response to Radiotherapy Combined With Targeted Therapy in Histiocytic Sarcoma Harboring Mutations in MAPK and PI3K/AKT Pathways

Background

Histiocytic sarcoma (HS) is a rare hematopoietic malignancy with an aggressive clinical presentation associated with a poor overall survival. To date, surgical resection, radiation therapy, and chemotherapy were often utilized for HS, but curative effects are rather disappointing.

Case Presentation

A 19-year-old female was referred to our hospital with a pathologic diagnosis of HS in December 2017. The patient had a severe airway obstruction resulting from a large mass (6.0 cm × 4.4 cm) arising from the left parapharyngeal space. She did not respond to cyclophosphamide, doxorubicin, vincristine, prednisone, and etoposide (CHOEP) chemotherapy, then she was switched to radiotherapy and crizotinib according to next-generation sequencing (NGS) results (mutations in MET and MAP2K1). The patient got a partial response after radiotherapy and crizotinib, then she switched to imatinib combined with thalidomide treatment. The patient got a long-term complete response from the treatment and is alive 44 months after initial diagnosis without disease progression. Further KEGG pathway enrichment analysis of NGS results from patient’s tissue revealed that phosphatidylinositol 3′ kinase (PI3K)/AKT and mitogen-activated protein kinase (MAPK) pathways were activated in this HS patient. We further performed experiments in vitro in a canine histiocytic sarcoma cell line DH82, in order to explore the possible mechanism of imatinib plus thalidomide in HS. Results of cell counting kit-8 (CCK8) assays showed that the proliferation activity of DH82 was significantly inhibited by imatinib but not thalidomide. Combined thalidomide and imatinib treatment did not improve the inhibitory effects of imatinib to DH82. Results of Western blot confirmed the inhibitory effects of imatinib on DH82 by targeting activation of MAPK and PI3K/AKT pathways.

Conclusion

Radiotherapy combined with targeted therapy guided by NGS may be promising, and further perspective clinical trial is warranted for the localized HS.

Primary histiocytic sarcoma in the brain with renal metastasis causing internal ophthalmoparesis and external ophthalmoplegia in a Maine Coon cat

Case summary

An 11-year-old neutered male Maine Coon cat was presented for investigation of anisocoria and depression. Neurological examination was consistent with a lesion at the level of the middle cranial fossa, and biochemistry was indicative of moderate renal functional impairment. MRI of the brain identified an extra-axial mass lesion at the level of the middle cranial fossa, T2-weighted hyperintense and strongly homogeneously contrast enhancing with dural tail. The cat was euthanased after 6 weeks of palliative treatment with corticosteroids. Histopathology and immunohistochemistry of the brain, the intra-cranial mass and the renal masses found on necropsy were consistent with histiocytic sarcoma.

Relevance and novel information

Central nervous system histiocytic sarcoma is a rare finding in cats. This original case report describes the neurological presentation, novel MRI characteristics and pathological findings of suspected primary histiocytic sarcoma affecting the brain with renal metastasis in a cat.

Successful Treatment of Incidental Histiocytic Sarcoma Concomitant with Laryngeal Carcinoma

Histiocytic sarcoma (HS) is an extremely rare non-Langerhans cell disorder with an aggressive course and limited treatment options. HS most often presents at an advanced clinical stage, with a limited response to chemotherapy and high mortality. No standard treatment has been established for HS. We herein describe the first case of HS concomitant with laryngeal carcinoma that was promptly diagnosed and successfully treated; the condition of the patient has remained stable for 4 years with no recurrence.

Histiocytosis

Histiocytoses constitute a heterogeneous group of rare disorders, characterised by infiltration of almost any organ by myeloid cells with diverse macrophage or dendritic cell phenotypes. Histiocytoses can start at any age. Diagnosis is based on histology in combination with appropriate clinical and radiological findings. The low incidence and broad spectrum of clinical manifestations often leads to diagnostic delay, especially for adults. In most cases, biopsy specimens infiltrated by histiocytes have somatic mutations in genes activating the MAP kinase cell-signalling pathway. These mutations might also be present in blood cells and haematopoietic progenitors of patients with multisystem disease. A comprehensive range of investigations and molecular typing are essential to accurately predict prognosis, which can vary from spontaneous resolution to life-threatening disseminated disease. Targeted therapies with BRAF or MEK inhibitors have revolutionised salvage treatment. However, the type and duration of treatment are still debated, and the prevention of neurological sequelae remains a crucial issue.

Histiocytic sarcoma following combination chemotherapy for primary mediastinal germ cell tumor: a diagnostic dilemma

Histiocytic sarcoma is considered an extremely rare condition. We herein report on a case of histiocytic sarcoma following combination chemotherapy for a primary mediastinal germ cell tumor in a 26-year-old Asian man who visited the General Medicine Department of a hospital with complaints of cough and high fever. Chest computed tomography (CT) imaging revealed a tumor (diameter 10.5 cm) in the anterior mediastinum, with no signs of metastasis, and CT-guided biopsy of the mediastinal tumor revealed the presence of some necrotic cartilages. The patient's serum α-fetoprotein (AFP) level was determined to be high at 160.4 ng/mL and a primary mediastinal non-seminomatous germ cell tumor was suspected, so the patient was referred to the Department of Urology. Despite the presence of severe thrombocytopenia, the patient was treated using a combination of chemotherapy and intermittent transfusion, which was able to normalize his serum AFP level. However, resection of the mediastinal tumor was unsuccessful due to persistent thrombocytopenia and the patient was subsequently transferred to our hospital for further examination and treatment. Despite management by hematologists, the condition of the patient did not improve; although his AFP level remained normal, the tumor increased in size and then metastasized to the liver and spleen. The general condition of the patient deteriorated and he died 9 months after his first visit. The patient was diagnosed with histiocytic sarcoma following a pathological autopsy. Due to the extremely rare incidence of histiocytic sarcoma, this condition should be a differential diagnosis and the appropriate tests must be conducted to give an exact treatment.

Nodal histiocytic sarcoma with prominent eosinophilic infiltration: expression of eotaxin-2 on tumor cells

Background

Histiocytic sarcoma (HS) is a rare neoplasm showing morphological and immunophenotypic features of mature tissue histiocytes. We report a patient with nodal HS exhibiting prominent reactive eosinophilic infiltration.

Case presentation

A 68-year-old man presented with intermittent left lower abdominal pain and weight loss over 3 months. A computed tomography scan revealed multiple abdominal nodules. Open biopsy of the mesenteric tumors was performed for definitive diagnosis. Histologically, the tumor was comprised of a diffuse noncohesive proliferation of pleomorphic large cells, including multinucleated cells. Neoplastic cells were positive for histiocytic markers (CD68, CD163, and LIGHT) and PD-L1 but lacked markers of Langerhans cells, follicular dendritic cells, and epithelial cells. Frequent reactive inflammatory cells were intermingled in the background. Interestingly, prominent eosinophilic infiltration was also noted. Spindle neoplastic cells were prone to be present around areas with little to no eosinophilic infiltration and exhibiting fibrosis and lymphatic vessel proliferation. Conversely, polygonal neoplastic cells were prone to be present around areas with relatively large amounts of eosinophilic infiltration without fibrosis or lymphatic vessel proliferation. Immunohistochemically, the tumor cells and reactive eosinophils expressed eotaxin-2 and eotaxin-3, respectively.

Conclusion

We revealed that eotaxins induced the selective migration of eosinophils into tissues in this case. These eosinophils may affect the tumor remodeling and tumor biology characteristics of HS, such as fibrosis and lymphatic vessel proliferation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13000-020-01061-4.

Leukemic Phase of Histiocytic Sarcoma of the Digestive System: A Rare Manifestation of a Rare Disease

Histiocytic sarcoma (HS) is a rare, malignant, and aggressive subtype of histiocytosis. We present an unusual case of aggressive HS presenting in the gastrointestinal tract and gallbladder that progressed after several lines of chemotherapy with a leukemic phase. We review the clinical, pathological, and molecular characteristics of HS in this case and review the literature on HS involving the digestive system as well as on overt leukemic phase of this disease. HS is often diagnosed at an advanced stage, and mortality is high. We discuss the therapeutic approach to patients with HS. We highlight the role of overexpression and somatic alterations in the RAF-MEK-ERK pathway in the pathogenesis of HS and discuss potential targeted approaches to treat these rare tumors.

A case report of metastatic giant sarcomatoid melanoma with BRAF V600E mutation: a complete response to targeted therapy

Sarcomatoid melanoma is an extremely rare pattern of malignant melanoma, and only few cases have been described throughout the literature. We herein report a case of a patient with newly diagnosed, metastatic giant sarcomatoid melanoma of the arm. The patient underwent surgical removal of the huge mass, and NGS sequencing demonstrated BRAF V600E mutation. In view of histological, immunohistochemical and molecular findings, a combined BRAF/MEK inhibitor (BRAF/MEK-i) therapy was prescribed as first line treatment. A complete response (over one year) to targeted therapy was obtained, and no adverse events have been reported. The patient maintained a full range of shoulder and elbow movements, and she is able to live independently and resume her daily activities. We therefore recommend that all patients with undifferentiated melanomas, sarcomatoid cutaneous malignancies or other mesenchymal tumours, should undergo BRAFV600E mutation testing.

BRAF mutation and its inhibitors in sarcoma treatment

The mitogen‐activated protein kinase (MAPK) signaling pathway plays a significant role in mediating cellular physiological activities, such as proliferation, differentiation, apoptosis, and senescence. This signaling pathway is composed of several major proto‐oncogenes of RAS/RAF/MEK/ERK, among which the BRAF proto‐oncogene, as one of the three members of the RAF family, has a higher mutation rate than ARAF and CRAF and has attracted extensive attention. Regarding the BRAF mutation, approximately 95% of BRAF mutations belong to the BRAF V600E mutation, which can enhance the expression of the MAPK signaling pathway and is thus related to the occurrence and development of various malignant tumors and has been successfully identified as a therapeutic target. Moreover, drug resistance to BRAF inhibitor treatment also appears to be an important issue. Considering the successful use of BRAF inhibitors in melanoma, we provide a brief overview of the BRAF mutations, including their basic structures and activation mechanisms, and the new classification method for BRAF mutations. Most importantly, we summarize the results of BRAF inhibitor treatment in different sarcomas. To overcome drug resistance to BRAF inhibitor treatment, we also outline the different mechanisms of drug resistance to BRAF inhibitor treatment and introduce the combination strategy of BRAF inhibitors with other targeted therapies.

Overview of « druggable » alterations by histological subtypes of sarcomas and connective tissue intermediate malignancies

We summarize herein the literature data about molecular targeted therapies in sarcomas and conjunctive tissue intermediate malignancies. For each clinical setting, the level of evidence, the mechanism of action and the target are described. The two major axes include (i) identification of subgroups of tumors with druggable alteration irrespective of the histological diagnosis (e.g. NTRK), and (ii) druggable target of pathway related to the physiopathology of the tumor: denosumab and bone giant cell tumor, imatinib and soft tissue giant cell tumor, mTOR inhibitor and PECOMA.

PTPN11 mutations in canine and human disseminated histiocytic sarcoma

In humans, histiocytic sarcoma (HS) is an aggressive cancer involving histiocytes. Its rarity and heterogeneity explain that treatment remains a challenge. Sharing high clinical and histopathological similarities with human HS, the canine HS is conversely frequent in specific breeds and thus constitutes a unique spontaneous model for human HS to decipher the genetic bases and to explore therapeutic options. We identified sequence alterations in the MAPK pathway in at least 63.9% (71/111) of HS cases with mutually exclusive BRAF (0.9%; 1/111), KRAS (7.2%; 8/111) and PTPN11 (56.75%; 63/111) mutations concentrated at hotspots common to human cancers. Recurrent PTPN11 mutations are associated to visceral disseminated HS subtype in dogs, the most aggressive clinical presentation. We then identified PTPN11 mutations in 3/19 (15.7%) human HS patients. Thus, we propose PTPN11 mutations as key events for a specific subset of human and canine HS: the visceral disseminated form. Finally, by testing drugs targeting the MAPK pathway in eight canine HS cell lines, we identified a better anti-proliferation activity of MEK inhibitors than PTPN11 inhibitors in canine HS neoplastic cells. In combination, these results illustrate the relevance of naturally affected dogs in deciphering genetic mechanisms and selecting efficient targeted therapies for such rare and aggressive cancers in humans.

Exceptional Responders in Oncology: A Systematic Review and Meta-Analysis of Patient Level Data

PURPOSE

We aim to systematically review and analyze the available literature on "exceptional responders" in oncology. We hypothesize that survival or patients with an exceptional response may be predicted based on clinical factors.

MATERIALS AND METHODS

A PICOS/PRISMA/MOOSE selection protocol was used to find studies that reported oncology patients with an exceptional response. A total of 333 initial articles were screened, and 76 articles were included, accounting for 85 patients. The primary outcome was survival after exceptional response therapy (ERT). The secondary outcome was survival since diagnosis. Univariate and multivariate analyses were conducted for both outcomes with 17 covariates.

RESULTS

The median age was 52 years (interquartile range, 35-66 y), 51.8% were male individuals, 18 (21.2%) had lung cancer, and 1 patient (1%) met all National Cancer Institute criteria for exceptional response. The most common treatment resulting in exceptional response was a form of chemotherapy (49.2%) followed by targeted therapy (26.8%) and radiation therapy (7.7%). The median time from diagnosis to initiation of ERT was 7.92 months (interquartile range, 0-24.72 mo). On multivariate analysis of survival after initiation of ERT, there were no predictors of exceptional response. On multivariate analysis of survival since diagnosis, predictors of prolonged survival included time between diagnosis and ERT initiation (hazard ratio, 0.52; 95% confidence interval, 0.32-0.87; P=0.0124) and single prior surgery versus none (0.08; 95% confidence interval, 0.01-0.98; P=0.04853).

CONCLUSIONS

There were no clinically apparent patient or treatment factors that predicted favorable survival following ERT; instead, reporting of exceptional response appears to be biased.

Identification of diverse activating mutations of the RAS-MAPK pathway in histiocytic sarcoma

Recent studies have demonstrated recurrent activating mutations involving the classical MAPK and PI3K signaling pathways in a large proportion of histiocytic neoplasms, such as Langerhans cell histiocytosis. However, very little is known about the molecular genetics of histiocytic sarcoma, a rare aggressive malignant neoplasm that shows pathologic characteristics of mature macrophages. Here we report the genomic characteristics of a large cohort of histiocytic sarcomas (n = 28) using a targeted next-generation sequencing approach to identify driver alterations. We identified recurrent mutations involving the RAS-MAPK signaling pathway (MAP2K1, KRAS, NRAS, BRAF, PTPN11, NF1, CBL) in a majority (57%) of histiocytic sarcoma cases and report a clinical response to a MEK inhibitor (Cobimetinib) in a patient with a NF1-mutated histiocytic sarcoma. A smaller subset of cases (21%) also showed mutations resulting in activation of the PI3K signaling pathway (PTEN, MTOR, PIK3R1, PIK3CA). In addition, the tumor-suppressor gene CDKN2A was the most frequently altered gene (46%). Further, a subset of histiocytic sarcoma cases shows striking molecular genetic similarities to B cell lymphomas, supporting a clonal relationship between B cell neoplasms and a subset of histiocytic sarcomas. These findings support a cooperative role for MAPK, PI3K, and cyclin-CDK4/6-INK4 signaling in the pathogenesis of histiocytic sarcoma and provide a rational basis for targeting these pathways.

Histiocytic Sarcoma: Review, Discussion of Transformation From B-Cell Lymphoma, and Differential Diagnosis

Context.—

Histiocytic sarcoma is a rare neoplasm of mature histiocytes with an aggressive clinical course that can arise de novo or from a low-grade B-cell lymphoma. In particular, chronic lymphocytic leukemia/small lymphocytic lymphoma is a very common malignancy in the Western hemisphere, and most cases of chronic lymphocytic leukemia/small lymphocytic lymphoma have an indolent course and behavior. However, 2% to 8% of chronic lymphocytic leukemia/small lymphocytic lymphoma cases transform. Histiocytic sarcomatous transformation is rare and portends poor prognosis.

Objective.—

To review the clinical features, morphology, and key points related to the differential diagnosis for histiocytic sarcoma. We discuss recent understanding of the biology underlying transformation.

Data Sources.—

University of Michigan case and review of pertinent literature about histiocytic sarcoma and morphologic differential diagnosis.

Conclusions.—

Histiocytic sarcoma is a rare histiocytic neoplasm that can arise as a result of transdifferentiation from low-grade B-cell lymphomas, and has a wide differential diagnosis including other histiocytic/dendritic cell neoplasms, myeloid neoplasms, lymphomas, melanoma, and carcinoma. However, some key morphologic and immunohistochemical features allow for accurate classification.

MARVELD1 depletion leads to dysfunction of motor and cognition via regulating glia-dependent neuronal migration during brain development

The establishment of functional neuronal connectivity is dependent on the neuronal migration and the accurate positioning of neurons in the developing brain. Abnormal neuronal migration can trigger neuronal maturation defects and apoptosis. However, many genetic bases remain unclear in neuronal migration disorders during brain development. In this study, we reported that MARVELD1-defected mice displayed motor and cognitive dysfunction resulting from aberrant neuronal migration during brain development. The laminar organization of the cerebral cortex and cerebellum in MARVELD1 knockout (KO) mice is disrupted, indicating impaired radial neuronal migration. Furthermore, we used the cerebellum as a model to explore the radial neuronal migration processes, and the results demonstrated that the proper neuronal migration depended on MARVELD1 expression in glial cells of the developing brain. MARVELD1 suppressed the expression of ITGB1 and FAK Tyr397 phosphorylation in glia-dependent manner. The inhibition of the MARVELD1/ITGB1/FAK signalling pathway in MARVELD1 KO mice could reverse the defects in neuronal migration in vitro. Our findings revealed that MARVELD1 regulated neuronal migration by mediating the formation of glial fibres and ITGB1/FAK signalling pathway. The depletion of MARVELD1 during mouse brain development led to the abnormity of motor and cognition functions.

Primary histiocytic sarcoma of the central nervous system: a case report with platelet derived growth factor receptor mutation and PD-L1/PD-L2 expression and literature review

Background

Histiocytic sarcoma (HS) is an aggressive malignant neoplasm. HS in the central nervous system is exceptionally rare and associated with a poor prognosis. This report documents a case of primary HS of the central nervous system with treatment including surgery, radiotherapy, and chemotherapy.

Case presentation

Our patient was a 47 year old female presenting with progressive ataxia, headaches, imbalance, nausea, vomiting, and diplopia. MRI showed a heterogeneously enhancing lesion approximately 2.9 × 3.0 × 2.3 cm centered upon the cerebellar vermis with mild surrounding vasogenic edema and abnormal enhancement of multiple cranial nerves. The patient underwent surgical debulking, which revealed histiocytic sarcoma with grossly purulent drainage. Staging revealed diffuse leptomeningeal involvement, primarily involving the brain and lower thoracic and lumbar spine. She underwent adjuvant radiotherapy to the brain and lower spine and was started on high dose methotrexate. However, she experienced progressive disease in the cervical and thoracic spine as well as pulmonary involvement. Genomic sequencing of her tumor showed a mutation in the platelet-derived growth factor receptor A (p.V0681) which could be targeted with Dasatinib. However, she did not tolerate Dasatinib and she succumbed to progressive disseminated disease eight months from original diagnosis. Our pathologic evaluation also revealed expression of PD-L1 and PD-L2 by tumor cells raising the potential therapeutic role for immune checkpoint inhibition.

Conclusions

This case provides an example of effective CNS control with resection and moderate doses of radiation therapy. A review of the literature confirms aggressive multidisciplinary treatment is the most effective treatment against this disease. In addition, genomic sequencing may play an important role in determining new therapeutic options. However, CNS histiocytic sarcoma remains an aggressive disease with a propensity for early widespread dissemination and few long term survivors.

Case of primary central nervous system histiocytic sarcoma with prominent proliferation of histiocytic cells between the trabeculae of reactive glial cells

Histiocytic sarcoma (HS) is an extremely rare malignant neoplasm that exhibits morphologic and immune-phenotype evidence of histiocytic differentiation. The disease most commonly involves the lymph nodes, gastrointestinal tract, skin, and soft tissue, as well as in the central nervous system (CNS) being relatively rare. Here we report a case of primary CNS HS with unusual histopathological characteristics. A 65-year-old woman presented with CNS HS in the left frontal lobe region, showing two distinct histological patterns. Approximately half of the lesion displayed histological characteristics typical of HS, including diffuse invasion of large round-to-ovoid pleomorphic cells, with mitotic figures (Ki-67 index: 30%) and coagulative necrotic foci. The other half exhibited prominent proliferation of histiocytic cells between the trabeculae of reactive glial cells, with rare mitotic figures (Ki-67 index: < 1%) and no necrotic foci. There were transitions between two morphologies. The HS tumor cells and the histiocytic cells between the trabeculae of reactive glial cells possessed nearly identical histomorphologic and immunophenotypic features, although the HS tumor cells showed a more pronounced degree of cytologic atypia and mitotic activity. To our knowledge, this is the first reported case of HS with prominent proliferation of the histiocytic cells between the trabeculae of reactive glial cells. Here we present the detailed histological, immunohistochemical, and molecular findings. Investigating cases of HS may provide insight into the pathogenesis of this disease.

Targeting MEK in a Translational Model of Histiocytic Sarcoma

Histiocytic sarcoma in humans is an aggressive orphan disease with a poor prognosis as treatment options are limited. Dogs are the only species that spontaneously develops histiocytic sarcoma with an appreciable frequency, and may have value as a translational model system. In the current study, high-throughput drug screening utilizing histiocytic sarcoma cells isolated from canine neoplasms identified these cells as particularly sensitive to a MEK inhibitor, trametinib. One of the canine cell lines carries a mutation in PTPN11 (E76K), and another one in KRAS (Q61H), which are associated with the activation of oncogenic MAPK signaling. Both mutations were previously reported in human histiocytic sarcoma. Trametinib inhibited sensitive cell lines by promoting cell apoptosis, indicated by a significant increase in caspase 3/7. Furthermore, in vitro findings were successfully recapitulated in an intrasplenic orthotopic xenograft mouse model, which represents a disseminated aggressive form of histiocytic sarcoma. Mice with histiocytic sarcoma xenograft neoplasms that were treated with trametinib had significantly longer survival times. Target engagement was validated as activity of ERK, downstream of MEK, was significantly downregulated in neoplasms of treated mice. Additionally, trametinib was found in plasma and neoplastic tissues within projected therapeutic levels. These findings demonstrate that in dogs, histiocytic sarcoma may be associated with a dysfunctional MAPK pathway, at least in some cases, and may be effectively targeted through MEK inhibition. Clinical trials to test safety and efficacy of trametinib in dogs with histiocytic sarcoma are warranted, and may provide valuable translational information to similar diseases in humans. Mol Cancer Ther; 17(11); 2439-50. ©2018 AACR.

Histiocytic cell neoplasms involving the bone marrow: summary of the workshop cases submitted to the 18th Meeting of the European Association for Haematopathology (EAHP) organized by the European Bone Marrow Working Group, Basel 2016

The bone marrow is a preferential site for both reactive and neoplastic histiocytic proliferations. The differential diagnosis ranges from reactive histiocyte hyperplasia in systemic infections, vaccinations, storage diseases, post myeloablative therapy, due to increased cell turnover, and in hemophagocytic lymphohistiocytosis, through extranodal Rosai-Dorfman disease to neoplasms derived from histiocytes, including histiocytic sarcomas (HS), Langerhans cell histiocytoses (LCH), Erdheim-Chester disease (ECD), and disseminated juvenile xanthogranuloma (JXG). One of the most important recent developments in understanding the biology of histiocytic neoplasms and in contributing to diagnosis was the detection of recurrent mutations of genes of the Ras/Raf/MEK/ERK signaling pathway, in particular the BRAF^V600E mutation, in LCH and ECD. Here, we summarize clinical and pathological findings of 17 histiocytic neoplasms that were presented during the bone marrow symposium and workshop of the 18th European Association for Haematopathology (EAHP) meeting held in Basel, Switzerland, in 2016. A substantial proportion of these histiocytic neoplasms was combined with clonally related lymphoid (n = 2) or myeloid diseases (n = 5, all ECD). Based on the latter observation, we suggest excluding co-existent myeloid neoplasms at initial staging of elderly ECD patients. The recurrent nature of Ras/Raf/MEK/ERK signaling pathway mutations in histiocytic neoplasms was confirmed in 6 of the 17 workshop cases, illustrating their diagnostic significance and suggesting apotential target for tailored treatments.

Histiocytic sarcoma in a child-successful management and long-term survival with cytoreductive surgery and hyperthermic intraperitoneal chemotherapy

Histiocytic sarcoma is an extremely rare tumor in children. It may occur sporadically or in association with other hematological malignancies. It arises most commonly in the lymph nodes but may occur anywhere in the body and clinical presentation is usually with advanced disease. Following tissue diagnosis and staging, management is with chemotherapy though there are no standard regimes. Surgery has been used successfully for local control. This is the first description of the use of peritonectomy and hyperthermic intraperitoneal chemotherapy to treat histiocytic sarcoma. The 4-year-old patient has been disease free for 6 years.

Primary central nervous system histiocytic sarcoma: A case report and review of literature

RATIONALE

Primary central nervous system histiocytic sarcoma (PCNSHS) is a rare lymphohematopoietic tumor with a histiocytic cell origin. To our knowledge, only 28 cases have been published in English and 2 cases in Chinese.

PATIENT CONCERNS

A 49-year-old Asian female presented to the hospital with a 2 month history of hypomnesia, odynophagia, and gait disorder. Physical examination demonstrated decreased lower extremity muscle strength. The patient denied a history of malignancy.

DIAGNOSES

Radiology demonstrated a lesion in parietal lobe with uniformenhancement. Histologic analysis showed pleomorphic tumor cells with a loose arrangement, effacing the normal brain tissue. The tumor cells exhibited abundant eosinophilic cytoplasm, highly atypical nuclei and predominant nucleoli. Immunohistochemistry revealed positive immunoreactivity for CD45, lysozyme, CD68, and CD163, and negative for pan-cytokeratin (CK), epithelial membrane antigen (EMA), glial fibrillary acidic protein (GFAP), CD3, CD20, CD1a, CD79a, CD138, oligodendrocyte transcription factor (olig2), CD15, melan-A, CD30, CD21, CD35, Human Melanoma Black-45 (HMB45), and anaplastic lymphoma kinase-1 (ALK-1). The diagnosis of PCNSHS was rendered.

INTERVENTIONS

The patient underwent complete surgical resection and adjuvant radiotherapy.

OUTCOMES

Follow-up information shows the patient died 8 months following the initial diagnosis.

LESSONS

PCNSHS is extremely rare with an aggressive clinical course. Immunohistiochemistry is necessary to make this diagnosis and to exclude other primary intracranial and lymphohematopoietic tumors. Further research is required to improve the outcome of patients with PCNSHS.

Expression of enhancer of zeste homolog 2 (EZH2) protein in histiocytic and dendritic cell neoplasms with evidence for p-ERK1/2-related, but not MYC- or p-STAT3-related cell signaling

EZH2 is an important enzymatic subunit of the epigenetic regulator polycomb repressive complex 2 (PRC2), which controls gene silencing through post-translational modification, and is overexpressed in various carcinomas and hematopoietic neoplasms. We found that the majority of cases of histiocytic and dendritic cell neoplasms, including histiocytic sarcoma, follicular dendritic cell sarcoma, Langerhans cell histiocytosis, and interdigitating dendritic cell sarcoma, show strong EZH2 expression by immunohistochemical staining, in contrast to benign histiocytic lesions and normal cellular counterparts, which did not show EZH2 expression, suggesting that this molecule may function as an oncogenic protein in these neoplasms. We correlated EZH2 expression with that of p-ERK1/2, MYC, and p-STAT3, potential regulators of EZH2, and found that 60-80% of these cases showed strong p-ERK1/2 expression, and only a minority of cases showed positivity for MYC or p-STAT3 in neoplastic cells. In cases of follicular dendritic cell sarcoma, Langerhans cell histiocytosis, histiocytic sarcoma, and interdigitating dendritic cell sarcoma with strong EZH2 expression, 90%, 89%, 70%, and 100% of cases showed co-expression of p-ERK1/2 with EZH2, respectively, while only a small percentage of these cases showed MYC or p-STAT3 co-expression with EZH2 (≤30%). These findings suggest that the p-ERK1/2 signaling cascade, but not the p-STAT3 and MYC signaling cascades, may regulate EZH2 expression in histiocytic and dendritic cell neoplasms, and that EZH2 and the p-ERK1/2 signaling cascade could serve as therapeutic targets for the treatment of these neoplasms. Interestingly, only a minority of cases of blastic plasmacytoid dendritic cell neoplasm exhibited high EZH2 expression, and only a minority of these cases showed p-ERK1/2 co-expression, suggesting that alternative mechanisms may contribute to tumorigenesis in this aggressive neoplasm.

A novel canine histiocytic sarcoma cell line: initial characterization and utilization for drug screening studies

BACKGROUND

Histiocytic sarcoma is a rare disorder in humans, however it is seen with appreciable frequency in certain breeds of dogs, such as Bernese mountain dog. The purpose of this study was to fully characterize a novel canine histiocytic sarcoma cell line, and utilize it as a tool to screen for potential therapeutic drugs.

METHODS

The histiocytic sarcoma cell line was characterized by expression of cellular markers as determined by immunohistochemistry and flow cytometry techniques. The neoplastic cells were also evaluated for their capability of phagocytizing beads particles, and their potential to grow as xenograft in an immunodeficient mouse. We investigated the in vitro cytotoxic activity of a panel of thirteen compounds using the MTS proliferation assay. Inhibitory effects of different drugs were compared using one-way ANOVA, and multiple means were compared using Tukey's test.

RESULTS

Neoplastic cells expressed CD11c, CD14, CD18, CD45, CD172a, CD204, MHC I, and vimentin. Expression of MHC II was upregulated after exposure to LPS. Furthermore, the established cell line clearly demonstrated phagocytic activity similar to positive controls of macrophage cell line. The xenograft mouse developed a palpable subcutaneous soft tissue mass after 29 days of inoculation, which histologically resembled the primary neoplasm. Dasatinib, a tyrosine kinase pan-inhibitor, significantly inhibited the growth of the cells in vitro within a clinically achievable and tolerable plasma concentration. The inhibitory response to dasatinib was augmented when combined with doxorubicin.

CONCLUSIONS

In the present study we demonstrated that a novel canine histiocytic sarcoma cell line presents a valuable tool to evaluate novel treatment approaches. The neoplastic cell line favorably responded to dasatinib, which represents a promising anticancer strategy for the treatment of this malignancy in dogs and similar disorders in humans.

Pediatric intracerebral histiocytic sarcoma with rhabdoid features: Case report and literature review

A 16-year-old boy presented with marked weight loss, weakness of the left extremities and dizziness of 2 months duration and vomiting for 2 days. Brain MRI showed an approximately 6.5 × 5.3 cm-sized huge heterogeneous enhancing mass located in the corpus callosum, extending into the lateral ventricle. Open biopsy showed that the lesion consisted of lymphoplasmacytes and plump histiocytes with rhabdoid morphology, which were stained with S-100 protein, CD68 (KP1) and negative for CD1a. Histiocytic tumor was initially diagnosed. Chemotherapy using methotrexate, 6-mercaptopurine, vinblastine, interferon-alpha and dexamethasone was performed. After 5 months, partial removal was done. Microscopically, plump and bizarre tumor cells as well as rhabdoid features were found. Occasional spindle cells and necrosis were also found. These cells were positive for CD163, CD68, lysozyme, CD4, INI-1 and BRG1. BRAF V600E mutation was detected. The lesion was finally diagnosed as histiocytic sarcoma. Radiotherapy (6000 cGy in 30 fractions) was done. Both cerebral and extracerebral histiocytic sarcomas have long been diagnosed by unclarified criteria; its rarity as well as previously unclarified criteria can easily lead to a misinterpretation. Histiocytic sarcoma of the CNS is exceptionally rare in children, associated with an exceptionally poor prognosis. To date, only seven cases of pediatric cerebral histiocytic sarcomas have been reported. The present case is the first pediatric case showing BRAF V600E-mutated intracerebral histiocytic sarcoma.

Histiocytic and dendritic cell neoplasms: what have we learnt by studying 67 cases

Tumors derived from histiocytic and dendritic cells encompass a large and heterogeneous group of neoplastic and reactive conditions, and their diagnosis is challenging both for pathologists and clinicians. Diagnosis is based on morphological and phenotypical findings, but hybrid features are not uncommon. Furthermore, recent studies uncovered the molecular mechanisms driving some of these tumors, improving diagnostic adequacy, and providing the basis for effective therapeutic breakthroughs.Sixty-seven cases were submitted to the accessory cell and histiocytic neoplasms session at the European Association of Haematopathology/Society for Hematopathology workshop 2016 held in Basel, Switzerland. The cases included histiocytic sarcomas (HS), Langerhans cell tumors (LCT), Erdheim-Chester disease, interdigitating dendritic cell sarcomas (IDCS), indeterminate dendritic cell tumors (IND-DCT), follicular dendritic cell sarcomas, and blastic plasmacytoid dendritic cell neoplasms. Rosai-Dorfman disease and, more rare, conditions such as ALK-positive histiocytosis were also submitted. These cases illustrated classical and unexpected features at morphological, phenotypical, and molecular levels, providing a valuable compendium for pathologists confronting with these tumors.The paper summarizes the most notable features of every single group of diseases, with comments about the most challenging issues, in the attempt to provide practical indications for their recognition.

Primary histiocytic sarcoma presenting as diffuse leptomeningeal disease: Case description and review of the literature

Histiocytic sarcoma is a rare malignant neoplasm arising most commonly in lymph nodes, intestinal tract, skin and soft tissue. The incidence of primary CNS histiocytic sarcoma is even rarer with a total of just 27 cases reported in the literature so far. Herein we describe the first autopsy case of histiocytic sarcoma presenting as a diffuse leptomeningeal disease in absence of a CNS tumor-forming parenchymal lesion. The clinical, pathological and immunophenotypic features are described and an updated literature review on primary CNS histiocytic sarcoma is included.